Fringe probing of gas-liquid interfacial film in a microcapillary tube.
An optical diagnostic technique has been developed to measure the gas-liquid interfacial film thickness in microcapillary two-phase flows. The spatial frequencies from the multiscattering measured with a CCD camera are used to determine the slug diameter and film thickness. It is found that, with an optimized optical orientation angle, the spatial frequency method shows great accuracy in the measurements. To demonstrate the capability of the newly developed method, a validation experiment was conducted in water-air and water-honey mixture-air two-phase flows. We measured the spatial frequency variations when the microbubble and slug were pulsating by utilizing a highly accurate signal processing technique and a five-point interpolation method. This newly developed optical method is easy to implement, and it will be a useful technique for two-phase flow measurements.